refactor: replace string-matching error checks with custom error classes

index.ts

@@ -7,6 +7,10 @@ import { Type } from "typebox";
 import * as path from "node:path";
 import { uriToPath } from "./src/client.ts";
 import { daemonDiagnostics, daemonRequest } from "./src/daemonClient.ts";
+import {
+  ServerNotFoundError,
+  UnsupportedExtensionError,
+} from "./src/types.ts";
 
 // Format Hover - Turn an LSP hover response into readable text.
 function formatHover(result: unknown): string {
@@ -202,6 +206,16 @@ function formatDiagnostics(result: unknown): string {
     .join("\n");
 }
 
+// Is Expected Error - Returns true if the error is an expected condition
+// (unsupported file type or missing server binary) that should be
+// suppressed rather than surfaced to the user.
+function isExpectedError(error: unknown): boolean {
+  return (
+    error instanceof UnsupportedExtensionError ||
+    error instanceof ServerNotFoundError
+  );
+}
+
 // Run LSP Request - Forwards to the daemon, which owns the long-lived
 // LspClient cache and handles didOpen/didChange syncing. The daemon
 // injects textDocument.uri from the file path, so we omit it here.
@@ -210,13 +224,27 @@ async function runLsp(
   method: string,
   params: Record<string, unknown>,
 ): Promise<unknown> {
-  return daemonRequest(filePath, method, params);
+  try {
+    return await daemonRequest(filePath, method, params);
+  } catch (error) {
+    if (isExpectedError(error)) {
+      return undefined;
+    }
+    throw error;
+  }
 }
 
 // Run LSP Diagnostics - Diagnostics arrive as a notification, so the
 // daemon has a dedicated op that waits for the next publish.
 async function runDiagnostics(filePath: string): Promise<unknown> {
-  return daemonDiagnostics(filePath, 1500);
+  try {
+    return await daemonDiagnostics(filePath, 1500);
+  } catch (error) {
+    if (isExpectedError(error)) {
+      return undefined;
+    }
+    throw error;
+  }
 }
 
 // Shared Parameters Schema - All position-based tools accept file + optional
@@ -412,11 +440,12 @@ export default function (pi: ExtensionAPI) {
     } catch (error) {
       // Silently fail - don't interrupt the flow
       // Only log if there's an actual error we care about
-      if (error && typeof error === "object" && "message" in error) {
-        const msg = (error as { message: string }).message;
-        if (!msg.includes("not found on PATH")) {
-          console.error("LSP auto-check failed:", msg);
-        }
+      if (!isExpectedError(error)) {
+        const msg =
+          error && typeof error === "object" && "message" in error
+            ? (error as { message: string }).message
+            : String(error);
+        console.error("LSP auto-check failed:", msg);
       }
     }
   });